Hi Toshi,
On 08/28/2013 05:38 AM, Toshi Kani wrote:
> On Tue, 2013-08-27 at 17:21 +0800, Gu Zheng wrote:
>> Hi Rafael,
>>
>> On 08/26/2013 11:02 PM, Rafael J. Wysocki wrote:
>>
>>> On Monday, August 26, 2013 04:43:26 PM Rafael J. Wysocki wrote:
>>>> On Monday, August 26, 2013 02:42:09 PM Rafael J. Wysocki wrote:
>>>>> On Monday, August 26, 2013 11:13:13 AM Gu Zheng wrote:
>>>>>> Hi Rafael,
>>>
>>> [...]
>>>
>>>>
>>>> OK, so the patch below is quick and dirty and overkill, but it should make the
>>>> splat go away at least.
>>>
>>> And if this patch does make the splat go away for you, please also test the
>>> appended one (Tejun, thanks for the hint!).
>>>
>>> I'll address the ACPI part differently later.
>>
>> What about changing device_hotplug_lock and acpi_scan_lock to rwsem? like the
>> attached one(With a preliminary test, it also can make the splat go away).:)
>
> I am curious how msleep(10) & restart_syscall() work in the change
> below. Doesn't the msleep() make s_active held longer time, which can
> lead the thread holding device_hotplug_lock to wait it for deletion?
Yes, but it can avoid busy waiting.
> Also, does restart_syscall() release s_active and reopen this file
> again?
Sure, it just set a TIF_SIGPENDING flag and return an -ERESTARTNOINTR error, s_active/file
will be released/closed in the failed path. And when do_signal() catches the -ERESTARTNOINTR,
it will change the regs to restart the syscall.
Thanks,
Gu
>
> @@ -408,9 +408,13 @@ static ssize_t show_online(struct device *dev,
> struct device_attribute *attr,
> {
> bool val;
>
> - lock_device_hotplug();
> + if (!read_lock_device_hotplug()) {
> + msleep(10);
> + return restart_syscall();
> + }
> +
>
> Thanks,
> -Toshi
>
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